Named after the two-faced Roman god Janus to reflect its dual-purpose design, researchers present a novel membrane system – a Janus channel of membranes (JCM) – capable of simultaneously separating oil and water from complex emulsions. The system addresses a critical challenge for sustainable water and oil reclamation across various industries. Separating oil and water from complex mixtures is essential for many scientific and industrial applications, such as wastewater treatment and biological sorting. Membrane technologies play a critical role in these processes. However, traditional membranes often remove only one component at a time, complicating further separation efforts and creating disposal challenges. This limitation is especially significant in treatment of oily wastewater, a common byproduct of both daily life and industrial activities – and widely recognized as one of the most serious threats to ecosystems and water sources. Although several treatment methods have advanced remediation and oil recovery from water, current membrane technology struggles to recover oil and water simultaneously from surfactant-stabilized emulsions.

Xin-Yu Guo and colleagues introduce a Janus channel of membranes system featuring a novel design that consists of a narrow, confined channel flanked by contrasting hydrophilic and hydrophobic membranes. As the emulsion mixture flows through this channel, pressure drives water molecules toward the hydrophilic membrane, allowing water to pass through while concentrating oil within the channel. The increase in oil density triggers hydrodynamic forces that encourage oil droplets to collide and merge, forming larger droplets with reduced surface energy, which can then pass through the hydrophobic membrane. This continuous process creates a feedback loop of enrichment, coalescence, and demulsification, allowing for the simultaneous, high-purity separation of oil and water without the concentration issues seen in traditional systems. In tests, Guo et al. show that the JCM system achieves impressive separation performance, with oil recovery of around 71% and water recovery of roughly 94% – both exceeding 99% purity. What’s more, unlike traditional hydrophilic membranes, which are limited to emulsions with less than 10% oil content, the JCM can process oil-in-water emulsions with oil content as high as 40%, still reaching over 50% water recovery and over 80% oil recovery. “The concept of Guo et al. goes beyond a simple oil-and-water separation from a complex mixture and can be applied to other types of challenging separations in large-scale industries,” write Xing Yang and Mohammad Hossein Jandaghian in a related Perspective. “Separation of water or glycerol from biofuels, valuable metals from mine tailings, and proteins and vitamins from dairy products are just a few examples.”